1. Technical Field
The present disclosure relates to imaging of an iris. Specifically, the present disclosure relates to a compact iris imaging apparatus used to capture an image of an iris at a standoff distance.
2. Description of Related Art
Imaging of an iris is often performed by illuminating a spatial volume that includes the face of a subject and then recording an image of an illuminated iris or irises. Infra-red light is often used for illumination because pigmentation in the iris is more transparent in the infra-red spectrum. The transparency of the pigmentation exposes the fine structures of the iris to the imaging system. The resulting image can be used for, as an example, biometric identification. Iris-based biometric identification typically requires a spatial resolution of 200 microns, or better, with a pixel resolution of approximately 60 microns for an ISO standard 19794-6-compliant image. In general higher spatial resolution leads to better matching performance by distinguishing the fine muscle structure of human irises.
Illumination systems used for iris imaging, particularly biometric imaging, regularly comprise multiple illumination sources that flood the capture volume (i.e., the volume in space over which the iris imaging system captures images) with a uniform or near uniform intensity of light. This type of arrangement facilitates adequate illumination of the capture volume and any irises within the capture volume.